Potential C and N mineralization and microbial biomass from intact and increasingly disturbed soils of varying texture

Potential C and N mineralization and soil microbial biomass C were determined following disturbance (i.e. drying and sieving) pretreatments in five soils varying in texture (30–350 mg clay gÿ1 soil) from the southern Piedmont USA. Soil disturbance by drying (i.e. rewetting following drying at 558C for 72 h) of intact soil cores resulted in a flush of C mineralization (70 % to 2.5-fold greater) during 0–3 d of incubation, but was not significantly dierent during 3–10 and 10–24 d periods compared with field-moist-intact soil cores. Soil disturbance by sieving resulted in greater C mineralization earlier than later in the incubation and led to significant immobilization of N of surface soil where respiration was highest. Increasing soil disturbance through smaller sieve openings resulted in a 10–60 % greater flush of C mineralization that may have been due to disruption of macroaggregates, which protected soil organic C. With a conditioning period of 10 d following rewetting of dried soil, soil microbial biomass C was unaected by drying or extent of sieving. Soil texture (i.e. clay content) did not interact with disturbance eects. Immobilization of N was predominant in surface soils (0–40 mm) of this bermudagrass pasture, where mineralizable C was very high. Carbon mineralization during 0–3 d was highly related (r 2=0.9620.04) to C mineralization during 0–24 d, basal soil respiration and soil microbial biomass C, although increasing soil disturbance (i.e. drying and extent of sieving) altered these relationships in a predictable manner. I conclude that dried and coarsely sieved soil compares favorably to field-moist-intact soil cores for estimating soil microbial biomass and potential activity in landscapes scoured by various degrees of erosion. Published by Elsevier Science Ltd. 1